1. Field of the Invention
This invention relates to a precast roof bearing block which is of substantially solid section and may be provided with reinforcing means.
2. Description of the Prior Art
In connection with underground mining activities it has long been known to provide means for securing the mine roof so as to reduce the risk of potentially life threatening cave-ins. It has been known to drill holes in the mine roof and to secure bearing plates by means of elongated roof bolts which are advanced into the drilled holes. As the roof bolt is advanced into the hole, the mine roof bearing plate is urged into intimate contact with the roof surface thereby transmitting a bearing force from the roof bolt head through the bearing plate to the roof to effect compression of the overlying strata. See generally U.S. Pat. Nos. 2,682 152; 3,224,202; 3,415,064; 3,521,454; 4,112,693 and 4,307,979.
It has been known to employ square or rectangular steel plates as bearing plates. One of the problems which has been encountered with such planar plates has been excessive deformation of the plates when load was applied. It has been suggested to provide integral stiffening means within the plates in order to resist undesired deflection under load. See, for example, U.S. Pat. Nos. 3,415,064 and 4,112,693. One of the problems with such constructions is that while the irregularities do serve to strengthen the plates, they result in a substantial reduction of the area of actual contact between the mine roof and the plate which, may be such as to reduce the area of contact by about 35 to 50 percent. Also, sharp edges of the steel plate tend to cut into soft rock if there is an uneven bearing surface. This serves to reduce the effectiveness of the roof support system.
U.S. Pat. No. 2,682,152 discloses a system wherein the grouting material which is introduced in the regions surrounding the anchor bolt is also, by means of a metal form member which remains in place, molded around the exterior of the roof hole. There is further provided a steel member which serves to resist the initial clamping load. As a result of the manner in which this construction is assembled the sharp edges of the channel member will tend to embed in the rock and consequentially a significant portion of the clamp load will be lost before the grouted material can harden. A further problem is that as a result of the need for the cap member to harden, a major portion of the clamp load will be lost allowing roof rock to sag, and, perhaps, fail prematurely, even before such solidification occurs. Finally, this patent requires special equipment to mix and place the grout.
There remains, therefore, a very significant need for a mine roof bearing block which will effectively establish the desired clamping preload so as to resist undesired deformations or cave-ins of mine roofs.